I created a team site in classic template just before the introduction of modern sites. It works fine for now except that I am having to rebuild one lists that still sometimes shows in classic edit mode while all other lists appear fine in the modern experience (i have been unable to identify the problem with that list). I do not know code at this time. I have built our sharepoint site with the typical available building blocks. Would it be better to start rebuilding the site and replace it with a modern team site? Right now it seems it would be a huge undertaking while it is constantly being updated of course - Unless... there is a way to transfer lists (with lookup fields intact) to a new site and do it quickly. I'm just wondering if the classic template will likely be unsupported in the future. Thus far I have been able to develop and maintain this site without code. I would like to keep it that way. This site is critical to our organization and I am responsible for it at this time. So, should I rebuild the site in modern teams or leave it the way it is? I would need consultant involvement if I leave it the same way and it becomes unsupported which is not ideal but okay if necessary.
Microsoft currently does not have a schedule to either deprecate or eliminate classic templates. With that being said, while there are a few reasons you might not want to use modern templates (customized search webparts being a bit one), no development efforts for new features are going to classic functionality.
I would suggest moving to modern where possible. You can use tools like Sharegate to migrate Lists/Libraries between sites.